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"Women twice as likely as men to experience anxiety, research finds," The Guardian reports. A new review that attempts to get a global snapshot of the prevalence of anxiety disorders identifies a number of vulnerable groups.

There are various types of anxiety disorder, but generally they involve feelings of unease, such as worry or fear, that can be mild or severe and affect daily life. Having an overwhelming sense of anxiety that "takes over your life" is described as having a generalised anxiety disorder.

There are many factors that can trigger an anxiety disorder, such as stress, physical conditions, genetic background and hormonal imbalances.

The researchers found that women, young people and those with other chronic diseases were disproportionally affected. Across countries, women were found to be twice as likely to be affected as men.

The researchers call for further research to be carried out on the illness, as well as investigating which type of interventions have the greatest benefit. There is also a need for further study of anxiety prevalence in developing and under-developed parts of the world, as there was a lack of representation.

Although feelings of anxiety at certain times are completely normal, you should see your GP if anxiety is affecting your daily life or causing you distress.

Where did the story come from?

The study was carried out by researchers from the University of Cambridge and Westminster City Council. It was funded by the UK National Institute for Health Research. The study was published in the peer-reviewed clinical journal Brain and Behavior. It is available on an open-access basis and is free to read online.

While the media coverage was generally accurate, both the Mail Online and The Times claimed that the reasons why younger women had higher levels of anxiety were down to many of them being working mothers. This claim seems to be based on opinions, rather than any hard evidence presented in the study.

What kind of research was this?

This was a systematic review that aimed to collate evidence from other systematic reviews which had explored the prevalence of anxiety, to describe the burden of disease across population subgroups.

As the researchers mention, anxiety disorders contribute to significant disability and impairment to quality of life, and are the most prevalent mental health conditions in Europe. They place increasing demand upon health services across the globe, and are recognised as important determinants of poor health. This is the first reported study to attempt to provide a comprehensive synthesis of the findings from reviews undertaken on the global burden of anxiety.

Systematic reviews are one of the highest levels of evidence, but they are only as good as the studies they contain. The included reviews varied widely in their methods, the studies they had included and populations examined. Due to this variation, the researchers did not attempt to carry out a meta-analysis of their findings. Instead, they report the findings across the individual reviews.

What did the research involve?

The researchers searched three literature databases up to May 2015 to identify systematic reviews and meta-analyses that had reported the burden of anxiety across the globe.

Reviews could have looked at any anxiety disorder, including generalised, social anxiety or obsessive compulsive disorder, and use any method to assess anxiety. The researchers specifically searched for reviews including individuals suffering from other medical or mental health conditions (chronic or infectious disease, psychiatric conditions, and addiction) as well as those from vulnerable populations. Reviews on the treatment of anxiety were excluded.

Two researchers assessed the quality of the reviews and eligibility for inclusion, and extracted data.

The reviews included studies of people of all ages, from young children to people of old age, with the overall number of studies and individual study sample sizes varying. The method of anxiety assessment also varied between studies, from structured and unstructured interviews to self-reported questionnaires.

What were the basic results?

Results from the 48 studies were gathered to describe the global distribution of anxiety disorders. The main results were as follows:

The general prevalence of anxiety disorders in healthy populations ranged from 3% to 25%.

Women were found to be twice as likely to be affected as men (female: male ratio of 1.9:1). This was consistently the case across different countries and co-existing health conditions.

Young adults under the age of 35 were also more often affected (2.5% to 9.1%).

Prevalence was found to be highest in North America (7.7%, 95% confidence interval [CI] 6.8 to 8.8) and in North Africa/Middle East (7.7%, 95% CI 6.0 to 10.0).

The lowest prevalence was found in East Asia (2.8%, 95% CI 2.2 to 3.4).

The prevalence was then described according to five common themes:

addiction

other mental and neurological disorders

chronic physical diseases

trauma

vulnerable population subgroups

They found that, compared to healthy populations, the prevalence was higher in individuals with chronic conditions, who had a prevalence ranging from 1.4% to 70%.

How did the researchers interpret the results?

The researchers concluded: "Despite epidemiologic advances in this field, important areas of research remain under- or unexplored. There is a need for further studies on the prevalence of anxiety disorders. These recommendations can serve to guide the research agenda, and most importantly, help develop tailored and timely interventions."

Conclusion

This systematic review of previously gathered data compiled evidence from 48 studies to describe the global prevalence of anxiety disorders, which are placing increasingly high demand upon health services across the globe. The review gives us a general picture of the prevalence of these conditions worldwide and notes several themes.

It found that anxiety disorders are common across all population groups, but women and young people seem to be disproportionally affected. Anxiety prevalence was also higher in individuals with chronic conditions, though it is not possible to say whether mental health problems could be a contributing factor or a consequence.

Reviews were assessed for eligibility against a validated quality assessment tool. However, the researchers highlight the large variability in the methods of the reviews and the studies they included, which makes comparison of prevalence figures between the studies difficult.

For example, there was wide variation between reviews in:

the overall number of studies they included and their sample sizes

the ages of participants, with some reviews looking at older individuals and some looking at children (aged 6+)

whether they were general population samples or those with specific physical or mental health conditions

the tools used to assess anxiety

whether they took account of other health, environmental or lifestyle factors

While this review is a useful indicator of the prevalence of anxiety disorders, it is unable to suggest causation – for example, why prevalence may be higher in women or younger adults. It is possible that this could be down to a complex interaction of biological and lifestyle factors. However, the direction of effect or the extent of influence of different factors remains unknown.

The researchers call for further research to be carried out on the course of the illness, as well as anxiety levels pre- and post-treatment. They also note the need for further study into developing and under-developed parts of the world, as there was a lack of representation of those areas, and for specific study into vulnerable subgroups of society.

Visit the NHS Choices Moodzone for more information about stress, anxiety and depression, and methods you can try to cope with and combat these feelings.